Spray gun

ABSTRACT

An electrostatic spray gun comprises a barrel; a hand grip at a support end of the barrel; an electrode at a material discharge end of the barrel; an electrical resistance member in the barrel having forward and rearward ends, the forward end being electrically connected to the electrode; a recess for receiving a high voltage cable, an end of which is inserted into the recess to be connected at a contact zone in the barrel. An electrical conductor extends between the contact zone and the resistance member for electrically connecting the resistance member to an inserted cable. The point of connection between the conductor and the resistance means is located rearwardly of the contact zone such that a portion of the resistance member can be located rearwardly of the contact zone to shorten the required length of the barrel.

United States Patent 1 Luderer et al.

[ Oct. 28, 1975 SPRAY GUN [73] Assignee: Firma Ernst Mueller KLG.,

Winnenden, Germany 22 Filed: Feb. 14, 1974 21 Appl.No.:442,321

[30] Foreign Application Priority Data Primary ExaminerRichard A. Schacher Assistant ExaminerRobert Saifer Attorney, Agent, or Firm-Burns, Doane, Swecker & Mathis [5 7] ABSTRACT An electrostatic spray gun comprises a barrel; a hand grip at a support end of the barrel; an electrode at a material discharge end of the barrel; an electrical resistance member in the barrel having forward and rearward ends, the forward end being electrically connected to the electrode; a recess for receiving a high voltage cable, an end of which is inserted into the recess to be connected at a contact zone in the barrel. An electrical conductor extends between the contact zone and the resistance member for electrically connecting the resistance member to an inserted cable. The point of connection between the conductor and the resistance means is located rearwardly of the contact zone such that a portion of the resistance member can be located rearwardly of the contact zone to shorten the required length of the barrel.

6 Claims, 3 Drawing Figures I "Will/liq US. Patent Oct. 28, 1975 Sheet10f2 3,915,380 v\ FIGI US. Patent Oct. 28, 1975 Sheet 2 of2 3,915,380

SPRAY GUN BACKGROUND AND OBJECTS OF THE INVENTION The invention relates to a spray gun for the electrostatic coating of objects with solid or liquid coating materials. A spray gun of this type typically comprises an insulating gun barrel, one end of which carries an electrode and the other end of which being provided with .a handle and inletfor a high voltage supply cable.

Inthe gun barrel an extended high voltage resistance is provided connecting the electrode with the high voltage cable.

Regarding electrical insulation characteristics in such handle-supported spray guns, a critical area is the end of the high voltage cable inserted into the gun. In order to prevent any dischargetaking place from this area to the gun handle, one generally proceeds in such a way that the high voltage cable isinserted so far into the gun barrel that the distance from the end of the cable to the handle is greater than the electrical flashover or sparking distance in air that can be calculated in the case of the voltage used. An elongated high-ohmic resistance memberleads from the end of the cable to the electrode of the gun via a socket connection. This type of constructiomhowever results in the fact that the gun barrel .must be of considerable length, corresponding at leastto the sum of the calculated flashover distance in air and the length of the high-ohmic resistance member. 4

Now to be sure, a gun construction has already been known in which the terminal sections of the cable and the high-hmic resistance are housed in a one piece jacket of insulating material of considerable length and thickness. In'this fashion, then, the connecting point between cable and high-ohmic resistance can be moved more closely to th e handle. However, in that case the slight saving in the length of the gun barrel is paid for by a considerable increase in construction expenditure and. by the requirement of having a handle of considerable, and thereby awkward dimensions. It is one objectof the invention to obviate or minimize disadvantages of the type previously discussed.

It is another object of the invention to minimize the barrel length of an electrostatic spray gun, while maintaining required flashover safety characteristics without significantly increasing construction'costs.

BRIEF SUMMARY OF A PREFERRED EMBODIMENT OF THE INVENTION According to the invention these objects are accomplished by the fact that thehigh voltage cable is carried in the gun barrel up to the area of the end of the barrel carrying the electrode/The end of the cable is connected to a high resistance member by means of a remm line which 'isinstalled in an insulated manner in the the other hand, the elongated high-ohmic resistance member, viewed purely spatially, lies essentially parallel to the high voltage cable in thegun barrel, whereby the above-mentioned return line constitutes the electric connection. Thus it is no longer required that the gun barrel has a length corresponding to the sum of the flashover distance and the extent of the resistance member. Rather, it will suffice that the length of the gun barrel corresponds to approximately the length of the high-ohmic resistance member or the flashover distance, depending on which of these two lengths is the greater. In practice, this means that the length of the gun barrel can be reduced to almost one-half the length of the customary barrels.

At the same time, one must take into consideration that the place of connection of the return line with the high-ohmic resistance member cause no difficulties from a point of view of insulation engineering. There'- fore, this connecting point can be closely adjacent to the handle, because the return line and the high-ohmic resistance member are firmly and permanently built-in parts of the gun. Thus, the fixed point of contact can be insulated by a poured-in insulating massfor example. The latter is in contrast to the connecting point of the cable which must be introduced subsequently into the finished gun and which must be connected in aplug type connection etc., in order to make possible a later replacement of the cable representing a closing element.

THE DRAWING In the drawing an embodiment of the invention is shown by way of example.

FIG. 1 shows, in partial longitudinal section, the construction of a spray gun according to theinvention.

FIG. 2 is a cross sectional view of the barrel 10 of FIG. 1, with a portion thereof broken away, depicting the diagonal orientation of the cable 14 and resistance member 16. I

FIG.3 is a partial longitudinal sectionalview of an alternate spray gun embodiment in accordance with the invention. I

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred spray gun shown in FIGS. 1 and 2 has a barrel designated as a whole by the numeral 10. At one end 10a (the front end) the barrel is provided with an electrode 11 and at its other end 10b (the rear end) with a pistol grip 12. The coating material that is to be sprayed-on is fed in by a pipe 13 to the passage 13' leading to the pistol grip and penetrating the pistol barrel l0 centrally up to the front connection of the pistol barrel. The reference numeral 14 designates. a high voltage cable which enters the pistol barrel at the rear end 10b and which is guided in a recess in the barrel 10 eccentrically to, and parallel to, the barrel axis. At an electrical contact zone in the barrel located in the front area 10a of the barrel 10, the end of the cable makes electrical contact with a plug contact 15. Furthermore, an elongated high-ohmic resistance member 16 is housed in the barrel 10, which member runs eccentrically to and parallel to the barrel axis and is arranged diagonally from the cable 14. The front end 16a of the resistance member is connected conductively with the electrode 11 in the customary manner, while the opposite end 16b of the resistance member is electrically connected with the plug contact 15 and thus with the cable end 14a. 'This connection is accomplished by means of a return conductor 17 which is connected firmly at one end with the resistance 16 and at the other end with the contact 15. The return line 17, as can be readily apparent from viewing the drawing, is installed in the form of an arc around the passage 13 in order thus to avoid any contact with the passage 13 (see FIG. 2) The point of connection between the line 17 and the end 16b of the cable 16 constitutes a permanent, fixed part of the spray gun and'thus can be insulated sufficiently to provide maximum safety.

In order to assure the required electric insulation, the barrel comprises an insulating material, whereby the cable 14, the resistance member 16 and the conductor 17 are installed in recesses or bores located in the barrel. The path ofthe electric current leads from the high voltage cable 14 via the contact 15, the conductor 17 and the high-ohmic resistance member 16 to the electrode 11. From an electrical point of view therefore, the high voltage cable and the high-ohmic resistance member 16 are electrically arranged in series, as is customary. From a point of view of space, however, the

cable 14 and the resistance member 16 are parallel, with a substantial part of the high resistance member .l6.being located rearwardly of the contact zone of contact 15.

Thus a high degree of safety is created for the operator with the shortest possible constructional length of the gun barrel 10. The critical point responsible in regard to possible flashovers to the grip 12, namely the contact point of cable 14a and plug contact 15, has been far removed from the grip 12. As mentioned previously, the contact point between the return line 17 and the rear end 16b of the resistance 16 lying closer to the grip 12 is relatively harmless, since this contact point is a fixed .and thus easily protectable, (i.e., insulatable) part of the spray gun.

As will be apparent, it is desirable that as much of the resistance member 16 as possible be disposed rearwardly of the contactlS. Note that in the preferred embodiment, the forwardmost end of the resistance member is substantially aligned or superposed with the contact in viewing a cross-section .of the barrel.

Naturally, the type of construction shown in the drawing can have variations. Thus, for example, ,it is nection, a spatial parallel arrangement be established in a manner accommodating a shortening of the length of the pipe. This embodiment is shown in FIG. 3 wherein a resistance member 16C is pipe-shaped and encases a concentrically arranged voltage supply cable 14C.

Electrical conductor 18C connects the resistance member 16C to the electrode 11.

' SUMMARY OF MAJOR ADVANTAGES In summary, a major advantage of the invention is provided by the-arrangement wherein a portion of the high resistance member, preferably as much thereof as possible, is disposed rearwardly of the contact zone where the high voltage cable is to make contact with the return line. A substantial savings in barrel length and construction cost can be realized thereby. Other advantages emanating therefrom, such as ease of gun manipulation, will be apparent to those skilled in the art.

Although the invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. In a spray gun for electrostatically coating objects with coating material, the spray gun comprising an electrically insulative barrel, an electrode disposed at a material discharge end of said barrel, a hand grip disposed at a support end of said barrel rearwardly of said electrode, elongate electrical resistance means disposed in said barrel and having forward and rearward ends, the forward end thereof being electrically connected with said electrode, and recess means in said barrel for receiving a voltage supply cable such that a contact end of said cable may be inserted into said barrel to an electrical contact zone; the improvement comprising:

electrical conductor means extending between said contact zone and said elongate resistance means for electrically connecting said elongate resistance means to the contact end of an installed supply cable, and

said electrical conductor means being electrically connectedto said elongate resistance means at a location disposed rearwardly of said contact zone suchv that a portion of said elongate resistance means is located rearwardly of the contact end of the installed cable.

.2. A spray gun according to claim 1 wherein said cable-receiving recess means and the elongate resistance means are disposed with their axesin spaced parallel relationship.

3.: A spray gun according to claim 2 wherein said cable-receiving recess and said elongate resistance means are disposed diagonally to one another relative to the axis of the barrel; and said conductor means having an arc-shaped course around a coating material passage in the barrel.

4. A spray gun according to claim 2 wherein the forwardmost end of said elongate resistance means is disposed substantially even with said contact zone relative to the cross-section of said barrel.

5. A spray gun according to claim 1 wherein said cable-receiving means and said elongate resistance means extend in a direction parallel to the axis of the barrel and said electrical conducting means comprising an electrical return line fixedly installed in said spray gun and being insulated at its point of contact to said elongate resistance means.

6. A spray gun according to claim I wherein said resistance means is pipe-shaped and concentrically encases the voltage supply cable. 

1. In a spray gun for electrostaticallY coating objects with coating material, the spray gun comprising an electrically insulative barrel, an electrode disposed at a material discharge end of said barrel, a hand grip disposed at a support end of said barrel rearwardly of said electrode, elongate electrical resistance means disposed in said barrel and having forward and rearward ends, the forward end thereof being electrically connected with said electrode, and recess means in said barrel for receiving a voltage supply cable such that a contact end of said cable may be inserted into said barrel to an electrical contact zone; the improvement comprising: electrical conductor means extending between said contact zone and said elongate resistance means for electrically connecting said elongate resistance means to the contact end of an installed supply cable, and said electrical conductor means being electrically connected to said elongate resistance means at a location disposed rearwardly of said contact zone such that a portion of said elongate resistance means is located rearwardly of the contact end of the installed cable.
 2. A spray gun according to claim 1 wherein said cable-receiving recess means and the elongate resistance means are disposed with their axes in spaced parallel relationship.
 3. A spray gun according to claim 2 wherein said cable-receiving recess and said elongate resistance means are disposed diagonally to one another relative to the axis of the barrel; and said conductor means having an arc-shaped course around a coating material passage in the barrel.
 4. A spray gun according to claim 2 wherein the forwardmost end of said elongate resistance means is disposed substantially even with said contact zone relative to the cross-section of said barrel.
 5. A spray gun according to claim 1 wherein said cable-receiving means and said elongate resistance means extend in a direction parallel to the axis of the barrel and said electrical conducting means comprising an electrical return line fixedly installed in said spray gun and being insulated at its point of contact to said elongate resistance means.
 6. A spray gun according to claim 1 wherein said resistance means is pipe-shaped and concentrically encases the voltage supply cable. 